CFRP 3-Point Bending Impact Test (Reference Standards: JIS K 7084:1993)

In recent years, carbon fiber reinforced plastics (CFRPs) have gained attention as strong, lightweight materials. To date, CFRPs utilizing thermosetting resins, which are not ideal in terms of cost, productivity, or potential for recycling, have been mainstream. As a result, they have been rarely used in transport vehicles except for aircraft. However, in the last few years, technology related to CFRPs utilizing thermoplastic resins has improved remarkably, so progress is being made in alleviating the above-mentioned disadvantages. In future, it is likely that CFRPs will be used in mass-produced vehicles, which will necessitate evaluations of the material. JIS K 7084 provides standards for testing machines in which a weight free-falls. In this experiment, we used the high-speed puncture impact testing machine, in which the speed is reduced only slightly on contact.

Measurements and Jigs

JIS K 7084 specifies the indenter radius as 5 mm, and the radius of each sample support as 2 mm. The test speed is 3.8 m/s. The standard dimensions of the sample are prescribed as follows.

Length (l) = 80 ± 1 mm
Width (b) = 10 ± 0.2 mm
Thickness (h) = 2 ± 0.2 mm

When tests are performed using a sample with the standard dimensions, the distance between supports (L) will be 60 ± 0.2 mm. JIS K 7084 specifies the test force sensor precision as ±5% of the test force value, and the sampling time as 10 μs max. This system satisfies the test force sensor precision for tests of 100 N or more. Sampling times of up to 1 μs are also possible.

Measurement Results

Fig. 2: Evaluation System for High-Speed
3-Point Bending Impact Tests

Fig. 3: Test Force – Displacement Curve

Table 1: Test Conditions
 Item Setting Value
 Test speed Load cell capacity   3.8m/s 10kN

Note: The reason for the fairly large noise immediately after the test starts is the collision between hard materials. Positioning a cushioning material on the supports and below the indenter is an effective way to suppress vibrational noise. Fig. 3 shows the test results with no cushioning material.

CFRP 3-Point Bending Impact Testing System
 Testing Machine  HITS-P10
 Striker  ø20
 Test jig  3-point bending test jig
 Software  High-speed impact testing software